This invention relates to an acoustical transfer characteristic controller for controlling the characteristics of acoustical transfer of audio reproduction output signals and, more particularly, to an acoustical transfer characteristic controller suitable for use as an apparatus for controlling the acoustical transfer characteristics of a sound field, such as a graphic equalizer or a surrounding processor.
Various controllers for processing reproduction signals supplied from audio reproduction systems to achieve acoustic effects with reality have been developed. Typically, a type of graphic equalizer is known which divides the reproduction frequency range into a plurality of frequency bands each of which can be controlled independently, and a type of surround processor is also known which is based on difference of signal transmission time for improving the presence.
The human ear has auditory sensitivity characteristics such that sounds in a low frequency range and a high frequency range become difficult to hear as the sound pressure level is reduced, as indicated by Fletcher Manson curves of FIG. 15. In the conventional controllers, however, only compensation is effected in accordance with a compensation curve irrespective of changes in the sound pressure level, which curve is previously adjusted and set.
On the other hand, a loudness control circuit which boosts low and high frequency levels when the sound volume is small is known as a means for compensating for the auditory sensitivity characteristics with changes in the sound pressure level. The compensation curve thereby obtained is definitely determined by circuit constants and cannot be finely adjusted.
Automatization of optimum adjustment for compensation for the sensitivity characteristics of the human ear may be studied based on providing the graphic equalizer or the surround processor with the same function as that of the loudness control circuit. For this automatization, however, each of the above described types of controllers requires a means for setting all possible conditions and a means for storing the corresponding characteristic patterns, and hence, a memory having a very large capacity.